Digital camera technology is being used in an increasing variety of mass-produced applications. A growing use of digital camera technology is incorporating or providing fixed-focus camera modules in consumer products such as wireless telephones, cell phones, personal digital assistants (PDAs), and other handheld electronic devices. While many consumers demand high-end functionality and quality, many consumers want the functions such as those provided by a digital camera but at affordable prices. For instance, it is estimated that that more than 65 percent of cell phones will include cameras. Additionally, there are many companies that produce consumer products such as cell phones and PDAs, and this competition requires that components including camera modules be produced with high quality but at acceptable costs with lower per unit material and assembly costs. This is especially true for products in which the camera is a secondary component such as when the product is primarily a communication device.
Fixed-focus camera modules used in many consumer products generally include a lens for focusing incoming light onto an image sensor that detects an image and converts it into an electrical signal representation. An image processor manipulates the image signal into an image that is stored or displayed on a display screen. Camera modules also include a chassis and enclosure for mounting the various electronic and optical components and for protecting the components from particulate and spurious light contamination.
Turning to FIG. 1, a conventional camera module 10 is illustrated that may be used to provide digital imaging functionality in a consumer product or application such as a wireless or cellular phone, tablet computer, and the like. The module 10 is a “double-die” version in which a number of dies or substrates are generally arranged on opposing surfaces of a printed circuit board assembly (PCBA) along a single axis. As shown, the module 10 includes a housing 22 (e.g., constructed of thermoplastic polymer such as polyvinyl chloride or PVC) having an internal cavity 24 with a first portion 26 that is adapted to receive a corresponding portion of a lens barrel 14 having at least one lens element 18 (via respective threaded portions 30, 34 on the housing 22 and lens barrel 14) and a second portion 38 that is adapted to receive and/or interconnect with a number of dies and other components that are generally collectively operable to receive and process incoming light passing through the lens element 18 to store and/or display a corresponding image. An infrared (IR) filter for filtering longer-wavelength radiation to limit noise created in an image sensor 58 is disposed within the internal cavity. Any appropriate transparent lens cover 19 may be disposed within or over an aperture 20 in the lens barrel 14 to allow the lens element 18 to receive light while protecting the lens element 18 and other components of the module 10 from particulates and other debris.
The module 10 includes a PCBA 42 (e.g., a multi-layer substrate) having first and second opposing surfaces 46, 50 for receiving one or more components and dies. An image sensor 52 including a first die 54 and an imaging chip 58 (e.g., CMOS chip) is electrically interconnected to the PCBA 42 by way of laying the first die 54 over the first surface 46 and bonding both ends of one or more pairs of wires 62 (e.g., gold) to respective contact pads 66, 70 on the first die 54 and the first surface 46 of the PCBA 42. An underfill such as a non-conductive paste (NCP) 72 is disposed between the first surface 46 and the first die 54 to further secure the first die 54 to the first surface 46.
A second die 74 (e.g., JPEG or graphics chip) is electrically interconnected to the second surface 50 of the PCBA 42 by way of a flip chip connection. More specifically, the second die 74 includes at least a pair of stud or solder bumps 78 that are spaced to align with a corresponding spaced pair of contact pads 82 on the second surface 50 of the PCBA 42. Upon flipping the second die 74 upside down and aligning the solder bumps 78 with the contact pads 82, flowing of the solder bumps 78 completes the electrical interconnect between the second die 74 and the PCBA 42. Again, NCP 73 is disposed between the second surface 50 and the second die 74 to further secure the second die 74 to the second surface 50. Furthermore, one or more surface mount technology (SMT) passive components 84 are electrically interconnected to the second surface 50 of the PCBA 42 via respective contact pads 86.
To assemble the module 10, the PCBA 42 is arranged so that the first die 54 is inserted into or otherwise disposed in the second portion 38 of the internal cavity 24 and faces the lens element 18 and an epoxy 88 is used to connect the PCBA 42 (e.g., via the first surface 46) to the housing 22. Also, the lens barrel 14 is threaded into the first portion 26 to a position whereby the lens element 18 is accurately focused on the imaging chip 58. As shown, the lens element 18, IR filter 90, imaging chip 58, first die 54, PCBA 42 and second die 74 are generally arranged so that their centers (not labeled) lie along an axis 92. The module 10 may be incorporated into a consumer product and appropriately interconnected to the system controller or processing unit of the product.
Mounting of first and second dies or substrates (e.g., first and second dies 54, 74) over opposing surfaces of a PCBA (e.g., over first and second surfaces 46, 50 of PCBA 42) has the drawback of reducing the surface area of the PCBA 42 that can be utilized by other dies and components. Furthermore, this arrangement has the negative effect of increasing the overall thickness of the module 10 (e.g., generally the distance between a top of the lens barrel 14 and the bottom of the second die 74) which reduces the ability of the module 10 to be incorporated into consumer products of ever-decreasing size.
As an additional corollary, with increased thickness comes an increased focal length (i.e., the distance between the lens element 18 and the imaging chip 58 assuming the lens element 18 is positioned to focus light rays on the imaging chip 58) of the optical arrangement of the module 10 which results in a corresponding increase in tilt management (i.e., the management of rotation of the lens plane relative to the image plane). Still further, as the image sensor 52 is mounted to the PCBA 42, the PCBA 42 must be precisely mounted to the housing 22 to correspondingly ensure that the imaging chip 58 is precisely aligned with the lens element 18 (e.g., along axis 92). In this regard, the interconnection between the PCBA 42 and the housing 22 is generally associated with relatively low tolerances.